Well, I had same problem with the taillights (rear hatch leak). I had water get into Tailight Failure Sensor and also corroded my taililights. I also took off my wing and plugged the wholes but, I replaced the third light with the bulb and threw some tape on it so the warning light would shut up. Anywho
I bought a used Tail Failure Sensor on ebay (**be sure you match the part numbers from your original one**) threw that on, yet still tail lights where not operating correctly. (i also checked all my relays and switches, which is a good idea).
What I finally did that fixed it was: I ripped all the tail lights out, got new pigtails, new bulbs, and some di-electric grease. I completely dissasembled it all cleaned and re-wired with new everything, minus the bulb holders (idk the proper name for them) i just cleaned them.
Threw some di-electric grease on the bulbs and new pigtails, installed and I was good to go everything works fine..If your new to wiring you might need some help..but thier is some helpful directions from supramania :
How-To:Repair tail lights - SupraMania
Dont know what path you will take but this is what worked for me